Automatic sweep electronic countermeasures system

ABSTRACT

1. An automatic sweep jamming system having a high duty cycle and rapid acquisition rate for jamming victim transmission systems comprising transmitter means capable of being swept very rapidly over a prescribed frequency spectrum for radiating electromagnetic energy, tuning control means coupled to said transmitter for sweeping said spectrum repetitively, receiver means capable of rapidly sweeping said prescribed frequency spectrum to detect electromagnetic energy from victim transmission systems, and means including said transmitter, said tuning control means and receiver means for automatically reducing the sweep rate of said transmitter means for a predetermined period in response to detection of victim electromagnetic energy.

United States Patent Winn [4 1 June 13,1972

AUTOMATIC SWEEP ELECTRONIC COUNTERMEASURES SYSTEM Primary Examiner-T. H.Tubbesing Attorney-Oscar B. Waddell, Frank L. Neuhauser, Dudley T. Readyand Irving M. Freedman [7 21 Inventor: Oliver H. Winn, Whitesboro, N.Y.

[73] Assignee: General Electric Company M AR CL IM [22] Filed: April 27,1960 1. An automatic sweep jamming system having a high duty cycle andrapid acquisition rate for jamming victim transmis- [211 App! 25l65 sionsystems comprising transmitter means capable of being swept very rapidlyover a prescribed frequency spectrum for [52] US. Cl ..343/18 Eradiating electromagnetic energy, tuning control means cou- [5 I Int.Cl- 0 pled to said transmitter for sweeping said spectrum repetitiveofSearch l 7 1y receiver means capable of sweeping said prescribedfrequency spectrum to detect electromagnetic energy from [56] Rfle'encesCited victim transmission systems, and means including said trans-UNITED STATES PATENTS mitter, said tuning control means and receivermeans for automatically reducing the sweep rate of said transmittermeans 2,567,261 William's "343/18 for a predetermined in response todetection of vi tim 2,862,203 1 H1958 Skaraeus et al ....343/l8electromagnetic energy 2,953,677 9/1960 Preisman ......343/I8 6 Clains,7 Drawing Figures f f /7 I I A? r r 4 6; 2/ I I 1 I 0 0//?C7'/0M4L l644417650 $3 2 32,322 ,332, cal/P1519 MAYA-R 574G:- 57465 I I l I I I-az4,wmva I I INPUT I I J4MM/A/6 I Iva/s: 7/7/6667? 5% TRANSMITTER Icomma; 26 a ar/aw l L $7465 I I i I I I I F I l /?!0 car/r001 620p! I I4/10 Pan :1? .SWPPZV 5746: awn-p L. J

CONT/L The present invention relates to electronic countermeasuressystems and more particularly to an improved countermeasures system inwhich there is included an automatic variable sweep technique toincrease the duty cycle of a swept jammer equipment.

Airborne electronic countermeasures (ECM) systems have been usedprimarily to jam unfriendly radar equipment. In general, the ECM jammerradiates a noise-modulated RF signal which enters the victim radar andrenders its indicator display useless. The jammer normally operates overa wide range of frequencies and the jammer frequency may be continuouslyvaried from some low value to a higher value. The RF frequency iscontrolled by servo control circuits included in the jammer equipment.The range of frequency variation is referred to as the sweep width.

In operation of present day ECM swept jammers, the frequency is usuallyvaried at either a sawtooth or triangular rate. A sawtooth variationoccurs when the frequency is continuously varied from a low frequency tosome higher frequency, then rapidly returned to the low frequency. Thissawtooth variation may be referred to as the slow sweep. The triangularvariation occurs when the frequency is continuously varied from a lowfrequency to some higher frequency, then brought back to the lowfrequency at the same rate or nearly the same rate. This triangularvariation may be referred to as the fast sweep." As the jammer frequencyis being swept, a random noise signal is supplied to the jammertransmitter. This signal amplitudemodulates the RF output.Electro-hydraulic tuning of the jammer oscillator produces the slow orfast sweep signal which causes variations in jamming frequency.

In such prior art electronic countermeasures systems the jammingfrequency remains within the victim radar band pass a relatively shorttime. No means are provided to indicate the location of the radarfrequency to be jammed and the system radiates for a relatively longtime while jamming for a relatively short time in a given cycle. Inorder for the system to be effective, noise modulation is appliedthroughout the operating cycle. Thus these systems have relatively lowduty cycles.

The present invention increases the duty cycle of prior art electroniccountermeasure systems by providing a system including an automaticsweep technique in which the jamming transmitter, used as a localoscillator, is swept very rapidly while looking for a victim signal.When the victim signal is detected, the sweep rate is changed and thetransmitter is caused to slow down when passing through the victim'sfrequency and jams effectively. Once the victims frequency is passed,the system is then returned to a search mode to look for another victimsignal. Thus, the duty cycle is proportional to the ratio of slow sweeptime to total sweep time and can be made extremely high.

Accordingly, one object of the invention is to provide a novelelectronic countermeasures system capable of effectively jamming aplurality of victim signals.

Another object of the invention is to provide an automatic variablesweep technique to increase the duty cycle and thereby improve jammingeffectiveness of electronic countermeasures systems.

A further object of the invention is to provide in a jamming systemautomatic means that sweeps very rapidly while looking for a victimsignal, and when the victim signal is detected the sweep rate is sloweddown during passage through the victim signal.

Still another object of the invention is to provide in a jamming systemautomatic means that sweeps very rapidly while looking for a victimsignal, slowly sweeps through the victim signal when detected, and thensweeps very rapidly while looking for other victim signals.

These and other objects and advantages of the present invention willbecome apparent by referring to the accompanying detailed descriptionand drawings in which like numerals indicate like parts, and in which:

FIG. 1 is a graphical representation showing the probability of jammingas a function of the duty cycle versus the number of jammers;

FIG. 2 is a graphical representation of an ideal sweep action vdesirable in electronic countermeasures system;

FIG. 3 is a graphical representation of the effect of various sweepratios included in electronic countermeasures systems;

FIG. 4 is a series of curves of intermediate frequency versus servodelay;

FIG. 5 is a simplified block diagram of the invention incorporatingautomatic sweep jamming techniques; and

FIGS. 6a-6b, taken together, are a detailed block diagram of a preferredembodiment of the invention shown in FIG. 5.

Anti-jamming techniques in modern radar and communication systems tendto decrease the effectiveness of low duty cycle swept jammers. Asmentioned hereinbefore, in present ECM systems the duty cycle is lowbecause the swept transmitter radiates power in portions of thefrequency spectrum in which there is no signal to jam.

The effectiveness of a countermeasures system operating against an enemyvictim radar is measured directly by the duty cycle of the jammersystem, the jammer duty cycle being defined as the ratio of:

t, is the time the radar is jammed, and

T, is the time for the jammer to sweep the frequency band.

It is to be observed that when D equals unity, the enemy radar would bejammed percent of the time.

Increasing the number of jammers operating against one radar effectivelyincreases the duty cycle. In FIG. 1 there is shown a graphical plotillustrating the probability of jamming versus the number of jammers.FIG. I shows the probability of jamming as a function of duty cycle aswell as the number ofjammers indicated as solid curves. The mathematicalexpression relating to the quantities is:

where:

P, is the probability of jamming,

D, is the duty cycle for one jammer, and

n is the number of jammers. I

Referring to the curves of FIG. 1, it will be noted that for a givenvalue of P the number of jammers required varies inversely as the dutycycle. In other words, if the duty cycle is doubled, the number ofjammers required is approximately half. Further, for a given number ofjammers operating in' a given frequency band, the probability of jammingvaries directly as the duty cycle. Therefore, an increased duty cycle isextremely desirable. I

The dotted curves shown in FIG. 1 illustrate the additional improvementobtained by equivalent synchronizing of the jammers. These dotted curvescan be represented by the expression:

P, nD 3 The curves indicate that the duty cycle is paramount to increased penetration capability.

From the description presented hereinbefore, there has been shown howincreased penetrationcapability can be obtained by increasing the dutycycle. It is extremely desirable to further enhance the effective dutycycle of the jammer. For example, consider a given spectrum which is Bmegacycles wide. N jammers operating in this band must locate all theenemy radars operating in the band and, after locating the radar, spendthe maximum time jamming them. Also, when a greater number of radars arepresent in a given spectrum than the number of jammers available,provision must be made to counter all the radars present at least partof the time, rather than leaving the excess radars unjammed. It is to beobserved that in order to accomplish this, continuous sweep of thejammer spectrum is necessary.

' Because of these requirements, the present invention is designed toyield a maximum duty cycle by sweeping the jammer spectrum rapidly untilthe radar is located. Upon locating the radar spectrum, the slow sweepspeed mode is inv itiated to jam effectively. After the radar spectrumis passed, the jammer returns to rapid sweep mode and searches for thenext radar spectrum and the operation is repeated.

The ideal sweep action desired is illustrated in FIG. 2 where the shadedareas represent enemy radar receiver bandpass. For a maximum duty cycle,the following ratio is required:

R, R, w (4) where,

R, is the fast sweep rate, and

R, is the slow sweep rate.

The ratio expressed in Equation (4) indicates that R, should be ofminimum value and R, should be as large as possible. As R, approachesinfinity, no time is required to sweep the region not occupied by theenemy radar. Clearly, this would be desirable but impossible to obtain.The effect of various sweep ratios is shown in FIG. 3. Each curve ofFIG. 3 illustrates the probability of jamming as a function of thenumber of jammers for a different fast sweep to slow sweep ratio. Thesecurves can be represented by the expression:

n,(r l) where:

P, is the probability of jamming,

n is the number of jammers,

b,, is the bandwidth of the jammer transmitter in megacycles,

B is the frequency spectrum to be swept in megacycles,

n,- is the number of radars to be jammed, and

r is the ratio of fast sweep to slow sweep.

In computing the curves of FIG. 3, the ratio of Blb has been taken as 40and n as l. The curves indicate the immense improvement that can beobtained by utilizing the novel variable sweep technique.

As an example, consider the case when one enemy radar is to be jammedeffectively for 80 percent of the total time. The problem is todetermine the number of jammers required to accomplish the desiredeffectiveness with the prior art electronic countermeasures equipmentversus the novel variable sweep technique. Substituting the values of P,0.8, r= l, B 400 Me, b,,= Me and n l in Equation (5) and solving for n,it is observed that the number ofjammers needed is equal to 63.5.

When the novel rapid automatic sweep techniques are employed, where r RR, 160 and substituting and solving for n, there results in arequirement for 0.9872 jammers. The ratio of R,/R,, as will be shownhereinafter, is limited to a maximum value because of inherent systemdelays. However, the improvement of approximately 65 to I constitutes amajor breakthrough in providing increased penetrating capabilities foreffective jamming.

As mentioned hereinbefore, the present invention is designed to increasethe duty cycle of a jamming transmitter by automatic variable sweepmeans. The oscillator of the ECM jamming transmitter is employed as areceiver local oscillator and is swept very rapidly while looking for avictim signal. When the signal is detected, the sweep rate is changedand the transmitter is caused to slow down in a track mode while passingthrough the victim signal for effective jamming. The system is thenreturned to a search mode to look for another victim. Included in theimproved ECM system are detection means that permit sufficient time tochange from the fast sweep mode to the slow sweep mode before jammingcommences.

In present day jamming equipments, the transmitter employs anoise-modulated, magnetron transmitting tube. This magnetron is tunedthrough a given frequency (such as shown in FIG. 2) by means of aservomechanism that drives the magnetron plunger. The servomechanism fordriving the plunger is described in an article entitled A NewElectro-Hydraulic High-Speed servomechanism by C. H. Willard and C. A.

Stemmer appearing in Volume 7, Number 5, of Automatic Control, datedNovember 1957 on pages 14-22. The present invention, a simplifiedembodiment of which is shown in FIG. 5, includes receiver means thatuses the continuous wave output from the magnetron as a local oscillatorsignal, thus allowing the transmitter and the receiver means to be tunedsimultaneously. In the absence of any enemy radar signal in the spectrumof the jammer, the system is tuned at a fast rate, R,. When an enemyradar is operating in the jammer spectrum, the local oscillator signalof the receiver will be constantly varying and heterodyning with anyfrequencies received. The receiver means is designed to respond to thedifference frequency, J};- This frequency is obtained when the magnetronCW frequency, hence the receiver local frequency, is located fmegacycles away from the radar frequency, f,., as the magnetron tunestoward the radar frequency.

The response signal from the receiver means is used as a trigger to thecontrol circuits that shape the command signal driving theservomechanism. Once the control circuit is triggered, the slope of theservo command signal is reduced to initiate a slow sweep of themagnetron. After an inherent system delay of 1, seconds, the actual slowsweep commences and continues for some predetermined time. At he end ofthe time interval, the control circuits change the slope of the servocommand signal, which returns the system to the fast sweep mode. Duringthe slow sweep mode, the transmitter magnetron is modulated with noiseto effect jamming. In addition, the receiver means is blanked-off theinstant the control circuits are triggered. The time interval for theslow sweep mode is long enough so that the system sweeps beyond thefrequency f of the enemy radar plus the difference frequency of thelocal oscillator signal f At the end of the time interval, the receivermeans is turned on. This method prevents the system from being triggeredby the image response.

From the discussion presented above, it is evident that the systemresponse to sweep command changes determines the intermediate frequency,in this case, 1],, to be used in the receiver means. The mathematicalexpression relating the intermediate frequency to system andenvironmental parameters is given by the following equation:

[F is the intermediate frequency in megacycles (Mc),

t, is the servo delay time in seconds,

12, is the enemy receiver bandpass in Mc,

b is the jammer transmit spectrum,

R, is the fast sweep rate in megacycle per second squared,

and

b,, is the jammer receiver bandpass in megacycles.

Reference will now be made to FIG. 4 in which there is shown a series ofcurves of intermediate frequency versus servo delay, computed by usingEquation (6). Each curve represents a constant value of fast sweep rate,R,. It is to be noted that an assumed enemy radar bandpass, h of 10 Meand jammer transmit spectrum, b 0f 15 Mc per second were used. A slowsweep rate of 25 Mc per second squared for a time interval of one secondwas also assumed. These assumptions are justified when operating againsta tracking radar. The maximum search (fast) sweep rate is determined bythe relation:

R,(max)=b,, PRF (7) where:

R, is the maximum search (fast) sweep rate in megacycles per secondsquared,

b,, is the jammer receiver bandpass, and

PRF is the pulse repetition frequency of the enemy radar.

The curves in FIG. 4 indicate the maximum fast sweep rate is set byenemy radar pulse repetition frequency (PRF) and the novel receivermeans bandwidth. The radar PRF is beyond the jammers control, and onceit is determined what type radar is to be jammed, that is, search ortrack, the PRF is set. Therefore, essentially, receiver bandwidth is theonly variable in the system. Also, high values of R, are desirable; butto increase R,, the receiver bandwidth must increase. When this is done,the set on accuracy deteriorates. In addition, for maximumeffectiveness, that is, increased duty cycle, the ratio R,/R should behigh and the IF of the receiver low. These two factors oppose each otherhowever in a system where servo delay is fixed.

It will be further noted that search radars will have an illuminationtime proportional to antenna bandwidth and inversely proportional toantenna rotation rate. Illumination time for the majority of searchradar at S-band would be in the order of O.l to 0.2 second. In a highsignal density area, if the slow sweep time were greater than theillumination times, the performance would be degraded. As previouslypointed out, whether a search or track radar is to be countered, thefast sweep rate is designed to be as high as possible if the IFfrequency and the servo delay is fixed. Therefore, when switched tocounter search radars, the slow sweep rate, R,,, increase will beinversely proportional to the change in slow sweep interval as requiredfor the illumination times of radars that will be encountered in thefrequency range of interest.

In FIG. 5 there is illustrated in block diagram form a simplifiedembodiment of the invention. As shown therein, a conventional jammingtransmitter 11 that radiates a noise-modulated RF signal, operable overa wide range of frequencies, the jamming frequency of which may becontinuously varied from some low value to a higher value and in whichthe RF frequency is controlled by a servo control and power supplycircuit (electro-hydraulic tuning means) is connected through aconventional directional coupler 13 to an antenna 15 for radiatingelectromagnetic waves. Directional coupler 13 in one embodiment is adouble-ridged, X-band coupler and provides a means for obtaining anattenuated RF sample of the unmodulated transmitter output. Receivermeans 12 are provided to monitor victim radar signals in order todetermine the frequency to be jammed and to provide a driving voltagewhich sweeps the transmitter frequency over the desired bandwidth. Inaddition, control and timing voltages are provided to slow down thesweep of the jamming transmitter when it is within the victim radarbandpass and to gate off the noise modulation to the jammer RF outputduring the search mode.

The receiver means 12 includes an antenna 17 for picking up victimsignals. This signal is applied to a balanced mixer stage 19 which iscoupled to an IF amplifier and detector stage 21, a video amplifierstage 25, a delay noise rejection stage 26, and control and timing stage27 including gate and trigger circuits. The gate and trigger circuitsare connected in circuit with a slope generator stage 29 which in turnis coupled to a servo drive mechanism 31 which is coupled to the plungerin the magnetron of transmitter 1 1.

In operation, the system as shown in FIG. 5 will perform in thefollowing manner. With no victim signal being received by antenna 17,the transmitter 11 sweeps over a prescribed frequency band, part of thetransmitter power is fed into balanced mixer 19 through directionalcoupler 13. Directional coupler 13 provides a means for obtaining anattenuated RF sample of the unmodulated output from transmitter 11. ThisRF sample is used by the receiver means 12 as a local oscillator signal.

The separate antenna 17 is required to supply signal energy from avictim signal to the balanced mixer 19. Directional coupler l3 extractsenergy from the transmitter transmission line for injection into themixer as local oscillator power. Thus, the receiver means is basically asuperheterodyne receiver which uses a transmitter signal as the localoscillator signal. When a victims signal is intercepted by receivingantenna 17, it is applied to the balanced mixer 19 and the transmitteris swept until it arrives at a frequency such that the difference fromthe transmitted and received frequency is equal to the intermediatefrequency, the difference signal. This difference signal, derived frommixer 19 is applied to an IF amplifier and detector stage 21 foramplification and detection. The detected output from stage 21 isamplified in video-amplifier 25 and then fed through a delay and noiserejection circuit 26 for application to the gate and timing circuits 27.The timing circuit turns on the noise modulation in the transmitter 11and programs the slope generator 29 to change the rate of sweep of thetransmitter. The transmitter sweep is thereby slowed and the noisemodulated power output from transmitter 11 is propagated by antenna 15at the victim signal frequency.

The purpose of the delay and noise rejection stage 26 is to allow thetransmitter 11, which is separated in frequency by the intermediatefrequency at the time of intercept to sweep close to the victims signalfrequency before the rate is changed. A blanking gate from gate andtiming circuit 27 is also applied to the IF amplifier stage 21 duringthe jamming period and maintains this amplifier in an off conditionuntil transmitter 11 sweeps past the image frequency. After jamming, thetransmitter is returned to the fast sweep mode. This cycle is repeatedwhen the same or another victim signal is intercepted.

Thus, it can be seen that the present system utilizes the magnetronoscillator of transmitter 11 as a superheterodyne receiver localoscillator. This oscillator is swept very rapidly while looking for avictim signal. When the signal is detected, the sweep rate is changedand the jammer transmitter 11 sweeps slowly through the victms signal,thereby increasing the length of dwell time." This slow rate of sweepingis maintained for a programmed length of time before the sweep speed ischanged back to the high speed search mode. The high search mode therebyminimizes the time spent searching, and the slow jamming rate maximizesthe time spent jamming with the result that the overall jamming dutycycle is greatly increased over the duty cycle obtainable with a simple,sweep jammer.

In order to more fully appreciate the invention as disclosedhereinbefore, there is shown in FIGS. 6a-6b a detailed block diagram ofapplicant's inventive concept. It will be recognized by those skilled inthe art that the circuits shown in FIGS. 6a-6b are well-known in the artand, therefore, no detailed explanation need be given for the particularcircuits included therein.

The receiver means 12 shown in FIGS. 6a-6b includes; directional couplerl3, mixer attenuator 19, IF amplifier and detector stage 21, videoamplifier stage 25, delay and noise rejection stage 26, control andtiming stage 27, and slope generator stage 29. In the followingdiscussion the assumption will be made that the frequency of the radarto be jammed (victim signal) is fixed.

As mentioned hereinbefore, the local oscillator signal to the receivermeans 12 is supplied by the RF oscillator in the jammer transmitter 11.This oscillator signal is attenuated by the directional coupler 13 andin an attenuator (not shown) included in mixer 19. The oscillator signalis then heterodyned with the signal from the victim radar received byantenna 17 and fed to mixer 19. Directional coupler 13 provides themeans for extracting an attenuated RF sample of the unmodulatedtransmitter output from the transmission line. This RF sample is used bythe receiver means as the local oscillator signal. After the localoscillator signal is attenuated by ,the directional coupler 13, itsamplitude is further attenuated by the mixer attenuator 19 to achievethe best signal-to-noise ratio.

Mixer 19 in one embodiment comprised a pair of matched crystals toassure local oscillator noise and video cancellation. The crystals arebiased in a forward direction so that the mixer conversion loss becomesless dependent upon the local oscillator level, the mixer operates withless than normal local oscillator power, and the mixer output impedanceis reduced making possible a better impedance match to the outputcoaxial cable. A 20 db attenuator (not shown) may be included in themixer assembly to further reduce the local oscillator power derived fromthe jammer transmitter 11 and makes possible a better impedance match tothe coaxial cable between mixer 19 and directional coupler 13.

IF amplifier and detector stage 21 provides a broad band pass with sharpcutoff. Sharp cutoff is desired in order that variations in receivedsignal amplitude will have little effect on the receiver signalinterception point as it searches. As seen in the drawing, IF amplifierand detector stage 21 includes a plurality of IF amplifier stages 39, acoupling amplifier 41, filter means 43 and detector means 45. The IFamplifiers 39 are staggered to produce proper IF response. In addition,the amplifier interstage coupling circuits (not shown) are peaked to thefrequencies indicated in the drawing. Each of the amplifiers is tuned toits separate frequency by a slug-tuned indicator (not shown). Filters 43are constant K-type filters with M-derived half-sections. These are usedto further increases the rate of attenuation above cutoff. Filters 43are driven by coupling amplifier 41.

The signal from filters 43 is fed into a detector 45. In one embodimentdetector 45 is a doubling type, half-wave diode detector and includes apair of crystal diodes forward biased by a voltage divider and through aload resistor (not shown). The detector efficiency variation caused bytemperature effects is minimized with this particular type arrangement.Further, the detector circuit is so arranged that the video output is anegative pulse. This negative pulse is the sensing pulse for the systemand initiates all other functions therein.

Video amplifier stage 25 includes a pulse amplifier 47 and driveramplifiers 49 and 50. Connected to the video amplifier stage 25 is adelay and noise-rejection stage 26 to which is coupled control andtiming stage 27. The circuits included within stages 25, 26 and 27 willhereinafter be referred to as pulse and timing circuits.

The pulse and timing circuits provide the following function controlsignals:

a. Stop delay-determines delay between receipt of pulse from videodetector and start of noise jamming;

b. Jam time-determines the time that noise modulation is turned on inthe jammer transmitter l l; and

c. Image blanking and track offset-produces the IF blanking pulse thatturns off IF amplifier 21 during jamming; the track pulse reverses thedirection of sweep at the end of the blanking time.

The detected output signal from detector 45 is amplified by amplifiers47 and 49 and fed to the noise rejection circuit included in stage 26.Said noise rejection circuit includes pulse level detectors 59, 61,cathode followers 63, 65, integrators 67, 69 and microsecond timers 71,73. The detected signal after amplification in amplifier 47 is alsoamplified in driver amplifier 50 and fed to noise rejection circuit. Ifthe noise rejection circuit does not reject the signal as noise, apositive pulse input is applied to the grid of trigger amplifier 75.

Multivibrator 77 produces the stop delay interval. The negative pulseoutput generated by trigger amplifier 75 passes through a diode (notshown) to the plate of one stage of multivibrator 77 and to grid of theother stage of said multivibrator. Thus, one half of multivibrator 77 isdriven beyond cutoff. The length of time that it remains cut off dependsupon the time constant set up by a stop-delay selector switch 77 andassociated circuits (not shown). The stop delay circuit is ineffectiveduring tracking operations. During sequential operation, the circuittime constants are so adjusted to provide a means of allowing the localoscillator frequency to continue sweeping until it reaches the victimfrequency. In order to initiate the jam time at the end of the stopdelay interval, a trigger is derived by conventional differentiatingmeans from the trailing edge ofthe stop delay pulse.

The circuits including cathode follower 78 and phantastron 79 withassociated components (not shown) form a phantastron time-basegenerator. A square, positive pulse is developed at the screen grid ofphantastron 79. This square positive pulse has a time base that is usedas the jam time. It is the time period during which slow tuning takesplace in the system. The duration of the phantastron output during trackoperation is determined by the time constant of the circuits and by thesetting of potentiometer 80. The duration of the phantastron outputduring sequential mode operation, with the switch 82 in the long"position, is determined by the time constant of the circuits and bycontrol 84. When switch 82 is in the short position, a much shorter jamtime is obtained.

The output of the phantastron during jamming time is coupled to cathodefollower 81. Cathode follower 81 supplies a negative voltage via diode83 to video amplifiers (not shown) in the jammer transmitter 11 when thesystem is not jamming in order to gate ofi the noise modulation. Duringjamming, this negative gate is removed. Also during jam time, thepositive output of cathode follower 81 is fed to the slope generatorstage 29 to ground the output of the 10 KC oscillator 127, therebystopping the fast sweep. After jam time, the positive output is removedand fast sweep is again initiated.

During operation of the phantastron, at the start of jamming time, thepositive pulse at cathode follower 81 is fed to the grid circuit ofdischarge tube 85. Discharge tube 85 acts as a Miller integrator.Capacitor 86 immediately charges from this low impedance source.Inversion takes place in the tube 85 which forces one half of Schmitttrigger circuit 87 into nonconduction. Schmitt trigger circuit 87 isbistable. Either half of trigger circuit 87 conducts at any given time,with an instantaneous change of state taking place upon triggering.

Prior to the occurrence of the jam timing pulse, the second half oftrigger circuit 87 is cut off. Because the plate voltage of the secondhalf of trigger circuit 87 is high, coupling diodes 89 are conductingand a rectifier associated with said coupling diodes (not shown) is backbiased. Receiver gain control circuits (not shown) set the voltage atthe grid of cathode follower 91, the cathode of which is connected tothe receiving circuits of the IF amplifier stage 21. During thephantastron pulse, the first half of trigger circuit 87 becomesnon-conducting due to the negative output of Miller integrator 85, andthe plate voltage rises from a pre-jam time value of volts, DC to avalue of volts, DC. When jam time is in effect, a jam indicator 93illuminates. The negative output voltage from cathode follower 91 is fedto the grids of coupling amplifier 41 and second IF amplifier 39, thusblanking the receiver IF strip.

Upon termination of the pulse, the amplifier circuit of integrator 85together with capacitor 86 in effect becomes a capacity multiplier,creating an effect identical to that of an equivalent capacitor of valueC X A, where A is the stage gain of integrator 85. Slow discharge ofcapacitor 86 takes place through a resistor (not shown). Therefore, thefirst half of circuit 87 remains non-conducting until the grid voltageof integrator circuit 85 drops sufficiently low. This drop occurs as themultiplied capacitor discharges. Restoration of receiver gain,therefore, is delayed following the jam time interval. This delay timeis known as the image blanking time and prevents retriggering due toresponse to the image frequency as the local oscillator resumes fastsweep. During sequential operation, this delay is adjustable by means ofan Image Blank potentiometer. During track operation, the image blankingtime depends upon the setting of Track Off-Set Control potentiometer 95.The setting of potentiometer 95 also determines the duration of fastsweep before the sweep is reversed. When the plate voltage of triggercircuit 87 suddenly increases, multivibrator 97 in slope generator stage29 changes states so that the direction of sweep is reversed. The imageblanking period is adjustable in time.

To provide radar blanking capability, a Miller integrator 99 isincorporated into the pulse and timing circuits to blank these circuitsto radiated pulses from other equipment in the aircraft. Normally, thegrid of the first half of integrator 99 is at a high negative potential.When blanking is desired, a positive blanking input pulse of limitedduration is applied from a circuit (not shown) to the integrator 99. Avery rapid negative-going sweep of 0.2 microsecond duration appears atthe plate of the integrator 99. The plate voltage bottoms until theblanking pulse is removed. At this time the plate voltage rises slowlyat an expotential rate dependent on the RC network included in theintegrator. The circuits remain insensitive for 2.0

microseconds after the pulse is removed, and recover to within 3 db offull sensitivity in microseconds or less after the trailing edge of theblanking pulse.

The noise rejection circuits included in stage 26 will now be describedin greater detail. Negative pulse outputs from the amplifiers 49 and 50are fed to the noise rejection circuit. The output from driver amplifier49 is applied to the grid of noise level detector 61. The other outputfrom driver amplifier 50 is applied to the grid of pulse level detector59. The positive outut pulses of detectors 61 and 59 are then applied tothe grids of cathode followers 65 and 63, respectively. The cathodeoutut of follower 65 is sent through a diode (not shown) to the grid ofMiller integrator 69 while the output of cathode follower 63 is fed tothe grid of Miller integrator 67 via a diode (not shown). Bothcapacitors connected between cathode follower 63 and integrator 67 andcathode follower 65 and integrator 69 immediately and simultaneouslydischarge from the low impedance sources presented by the cathodefollowers. Inversion takes place in integrators 69 and 67 driving thegrids of timers 73 and 71 beyond cutoff. The circuits associated withtimers 73 and 71 comprise bistable Schmitt trigger circuits. The circuit73 acts as a 120-microsecond timer while the circuit 71 functions as al40-microsecond timer. The timing is determined by the constants ofintegrators 69 and 67. The plate voltages of tubes 73 and 71 risesharply as a result of the abrupt cut-off of their grids.

It is to be observed that integrators 69 and 67 remain nonconductinguntil the grid voltages of tubes 65 and 63 drops sufficiently low whilethe multiplied capacitor discharges. The plate of tube 73 is triggeredby its increasing grid voltage approximately 120 microseconds after thepulse input to cathode follower 65. The plate voltage drops to itsinitial voltage. The rising grid voltage of tube 71 does not trigger itsplate until approximately 140 microseconds after the pulse input tocathode follower 63. During the l20-microsecond interval, no conductiontakes place through rectifier 101 while conduction does occur throughrectifier 103. The junction of capacitor 105 and resistor 107 is held atapproximately 100 volts positive. Between 120 microseconds and 140microseconds after the pulse, neither rectifier 101 nor 103 isconducting and the junction of capacitor 105 and resistor 107 returns to+150 volts. The charge of voltage is coupled through capacitor 105 as a50-volt positive pulse to trigger the stop delay or trigger amplifier75. After 140 microseconds, conduction occurs through rectifier 101 butnot through rectifier 103 and consequently, the junction of capacitor105 and resistor 107 returns to its normal value of +100 volts.

The positive output pulse developed at the plate of timer 73 is alsoapplied to diode 109 as back biasing and prevents the negative pulseinputs from driver 50 from entering the integrating and timing circuitsof the l40-microsecond network. Since capacitor 105 charges and apositive output from 73 occurs each time a pulse is applied to thecapacitor, then pulses which are less than 120 microseconds apart areprevented from entering the 140-microsecond circuits to restart thetimer. Since the 120 microseconds timer 73 can be restarted, and theinput to the l40-microsecond timer 71 is blanked and this timer cannotbe restarted, the output pulse from the circuit 73 can extend beyond thecompletion of the 140- microsecond pulse. In this case, a trigger willnot be produced. Thus, any pulse repetition frequency higher thanapproximately one one hundred and twentieth microseconds will nottrigger the stop delay.

The slope generator stage 29 generates the waveforms necessary for rapidand slow tuning of the system. The most important circuit of thisgenerator is the bistable flip-flop consisting of both halves ofmultivibrator 97 and associated components. During search operation, asthe system searches for a victim signal, this flip-flop produces squarewaves at each plate.

Since the plate voltage of the conducting tube is low, there isimpressed a low voltage on the grid of the cutoff tube; whereas the highvoltage at the plate of the cutoff tube results in a high voltage on thegrid of the conducting tube. Thus, a stable state is maintained. If animpulse is placed on either grid in the proper polarity to upset thisstable condition, regenerative action rapidly transfers the conductingstate from one tube to the other. For instance, if a negative pulse isinjected into the grid of the conducting tube, a decrease in platecurrent results with consequent increase in plate voltage. Thisincreased plate voltage increases the grid voltage on the nonconductingtube causing conduction to start which results in a lower plate voltageon that tube. The lower plate voltage on the tube which is beginning toconduct causes a further reduction of grid voltage on the tubeoriginally receiving the negative trigger. This regenerative actionrapidly causes the first tube to be cut off and therefore, the transferto the second stable state is complete.

The other circuit which is part of the overall bistable circuit is avoltage comparator commonly known as the multiar." This circuit employsa regenerative loop to produce a pulse when two input voltages areequal. Two such comparators are used.

The output from multivibrator 97 is modified by clipper circuit 111. Thevoltage at the cathode of circuit 111 produces a 35 volt reference forthe clipper circuit. Included in said clipper circuit are a plurality ofdiodes. These diodes provide for clipping the output of themultivibrator 97 at 0 and 35 volts. This is done to eliminate theeffects of any unbalance between vacuum tube sections. Further,circuitry included in clipper circuit 111 performs a gating function toallow a change in the state of flip-flop 97 when a track off-set triggeris received.

The rate of change of the jamming frequency of the system is controlledby a jam rate selector switch during sequential jamming and a track jamrate selector switch during track jamming. For simplicity, both switchesare shown as one in the drawing and designated 113. A search ratecontrol in the form of potentiometer 115 selects the amplitudecorresponding to the rapid sweep.

An integrator of the Miller or amplified-time constant type is includedin slope generator stage 29. Because the circuit components within theintegrator are fixed, an output results which depends only upon theinput waveform. When a square wave is used for input, the character ofthe output depends only on the amplitude of the input. Because thiscircuit integrates the input square wave, a triangular output. waveresults. Integrator 117 includes capacitor 119, differential amplifier121, differential amplifier 123, cathode follower and associatedcircuits. Component values and input amplitudes may be selected whichdetermine the slope of the output triangular wave.

Diode bridge circuit 117 is used as an electronic switch which is openonly when a signal has been intercepted and when slow tuning is desired.Its action is as follows. 10 kc oscillator 127 and amplifier 131comprise an audio oscillator and amplifier, respectively. The l0 kcvoltage produced is transformer-coupled to a full wave bridge rectifier133. As the receiver portion of the system tunes rapidly, this voltageis present and the integrator bridge circuit conducts through couplingneon glow tube 135. Thus, the rate of tuning (triangle slope) isdetermined by the amplitude of input preset potentiometer 115 and aresistor associated therewith (not shown) connected to bridge circuit117.

During the jamming time interval, the positive output of cathodefollower 81 is routed through control gate 129 which includes a pair ofdiodes, to ground. This effectively connects the output of theoscillator 127 to ground. Therefore, the oscillator input to the bridgerectifier 133 is removed. The coupling neon lamp 135 immediatelyextinguishes. With electronic switch 117 open, the integrator assemblyreceives a different amplitude of input, selected by jamming switches113. The slope of the output triangular wave at cathode follower 125then becomes very small to slow tune the oscillator during jam time.

A linear variation in voltage with respect to time is achieved bycharging or discharging capacitor 1 19 at a constant current rate. Theintegrator circuit regulates this action. Since the grid of differentialamplifier 121 draws no current, all the current charging or dischargingcapacitor 119 most pass through a resistance (not shown) in series withthe grid of amplifier 121. If a positive square wave from multivibrator97 is applied to resistors associated with amplifier 121, the gridvoltage of amplifier 121 would ordinarily tend to raise the capacitorcharging time passing through the resistors. This rise is amplified bydifferential amplifiers 121 and 123 and fed back via cathode follower125 in the negative direction to the opposite side of capacitor 119.This amplified wave produces a current very nearly equal in magnitudeand in opposition to the original current through the resistorsassociated with the grid circuit of amplifier 121. Consequently theinput grid voltage rise is extremely small and a nearly constant currentflows into capacitor 1 19, producing a linear rise in capacitor voltage.Since the change in grid voltage is small and linear, the feedbackvoltage from cathode follower 125 must also be linear and is used asoutput. Exactly the same analysis is applicable in the reverse directionas the negative portion of a square wave is applied.

During jam time, the charging resistance for integrating capacitor 119is increased by the insertion of additional resistance associated withswitch 1 13. Consequently, the voltage variation with respect to timeand, therefore, the frequency variation rate is decreased considerably.

The circuit comprising chopper modulator 137, transformer 139 andassociated circuits acts as an electronic chopper. During alternatehalf-cycles of 400 cycles per second voltage produced at the primary oftransformer 139, no triangular output voltage appears at the primary oftransformer 141 and the triangular waveform is chopped. The width trimmaximum potentiometer 143 at the secondary of transformer 141 determinesthe fast sweep width by trimming the voltage to be sent to the magnetronservo-control circuit in the jamming transmitter, thereby determiningthe maximum range of frequencies which the magnetron will cover. Centerfrequency balance control potentiometer 145 is used to balance theheights of adjacent peaks of the modulated chopped triangular waveformby adjustment of the voltage at the center top of the primary winding oftransformer 141.

As mentioned hereinbefore with respect to FIG. 5, there has beenprovided an improved countermeasures system in which there is includedan automatic variable sweep technique to increase the duty cycle of aswept jammer transmitter. While particular embodiments of the inventionhave been shown and described herein, it is not intended that theinvention be limited to such disclosure, but that changes andmodifications can be made and incorporated within the scope of theclaims.

What is claimed is:

1. An automatic sweep jamming system having a high duty cycle and rapidacquisition rate for jamming victim transmission systems comprisingtransmitter means capable of being swept very rapidly over a prescribedfrequency spectrum for radiating electromagnetic energy, tuning controlmeans coupled to said transmitter for sweeping said spectrumrepetitively, receiver means capable of rapidly sweeping said prescribedfrequency spectrum to detect electromagnetic energy from victimtransmission systems, and means including said transmitter, said tuningcontrol means and receiver means for automatically reducing the sweeprate of said transmitter means for a predetermined period in response todetection of victim electromagnetic energy.

2. An automatic sweep jamming system having a high duty cycle and rapidacquisition rate for jamming victim transmission systems comprisingtransmitter means capable of being swept very rapidly over a prescirbedfrequency spectrum for radiating electromagnetic energy, tuning controlmeans coupled to said transmitter for sweeping said spectrumrepetitively receiver means capable of rapidly sweeping said prescribedfrequency spectrum to detect electromagnetic energy from victimtransmission systems, and means including said transmitter, said tuningcontrol means and receiver means for automatically reducing the sweeprate of said transmitter means for a predetermined period in response todetection of victim electromagnetic energy and returning saidtransmitter and receiver means to the rapid sweep rate after saidpredetermined period.

3. An automatic sweep jamming system having a high duty cycle and rapidacquisition rate for jamming victim transmission systems comprisingtransmitter means including an oscillator capable of being swept infrequency very rapidly over a frequency spectrum for radiatingelectromagnetic energy, tuning control means coupled to said transmitterfor sweeping said spectrum repetitively, receiver means including saidoscillator capable of rapidly sweeping said frequency spectrum to detectelectromagnetic energy from victim transmission systems, and means forautomatically reducing the sweep rate of said transmitter and receivermeans in response to detection of electromagnetic energy from victimtransmission systems.

4. An automatic sweep jamming system having a high duty cycle and rapidacquisition rate for jamming victim transmission systems comprisingtransmitter means including an oscillator capable of being swept infrequency very rapidly over a frequency spectrum for radiatingelectromagnetic energy, tuning control means coupled to said transmitterfor sweeping said spectrum repetitively, receiver means including saidoscillator capable of rapidly sweeping said frequency spectrum to detectelectromagnetic energy from victim transmission systems, and means forautomatically reducing the sweep rate of said transmitter and receivermeans in response to detection of electromagnetic energy from victimtransmission systems and returning said transmitter and receiver meansto the rapid sweep rate thereafter.

5. In combination with an electronic countermeasures transmittingequipment which is capable of being continuously varied in frequencyfrom a low value to a higher value to radiate jamming signals over arange of frequencies for counten'ng victim transmission systems, meansfor automatically sweeping said transmitting equipment sure that thesweep rate of said equipment is slowed down while passing throughdetected signals from victim transmissions and the sweep rate isreturned to its normal sweep rate, said means comprising receiver meanscapable of rapidly sweeping a range of frequencies to detect signalsfrom victim transmission systems, and means for automatically reducingthe sweep rate of said transmitting equipment in response to detectionof said victim signals.

6. In combination with an electronic countermeasures transmittingequipment which is capable of being continuously varied in frequencyfrom a low value to a higher value to radiate jamming signals over arange of frequencies for countering victim transmission systems, meansfor automatically sweeping said transmitting equipment such that thesweep rate of said equipment is slowed down while passing throughdetected signals from victim transmissions and the sweep rate isreturned to its normal sweep rate, said means comprising receiver meansincluding the oscillator of said transmitting equipment capable ofrapidly monitoring a range of frequencies to detect signals from victimtransmission systems, and means for automatically reducing the sweeprate of said transmitting equipment in response to detection of saidvictim signals and returning the sweep rate to its normal sweep ratewhen no signals are detected.

1. An automatic sweep jamming system having a high duty cycle and rapidacquisition rate for jamming victim transmission systems comprisingtransmitter means capable of being swept very rapidly over a prescribedfrequency spectrum for radiating electromagnetic energy, tuning controlmeans coupled to said transmitter for sweeping said spectrumrepetitively, receiver means capable of rapidly sweeping said prescribedfrequency spectrum to detect electromagnetic energy from victimtransmission systems, and means including said transmitter, said tuningcontrol means and receiver means for automatically reducing the sweeprate of said transmitter means for a predetermined period in response todetection of victim electromagnetic energy.
 2. An automatic sweepjamming system having a high duty cycle and rapid acquisition rate forjamming victim transmission systems comprising transmitter means capableof being swept very rapidly over a prescirbed frequency spectrum forradiating electromagnetic enErgy, tuning control means coupled to saidtransmitter for sweeping said spectrum repetitively receiver meanscapable of rapidly sweeping said prescribed frequency spectrum to detectelectromagnetic energy from victim transmission systems, and meansincluding said transmitter, said tuning control means and receiver meansfor automatically reducing the sweep rate of said transmitter means fora predetermined period in response to detection of victimelectromagnetic energy and returning said transmitter and receiver meansto the rapid sweep rate after said predetermined period.
 3. An automaticsweep jamming system having a high duty cycle and rapid acquisition ratefor jamming victim transmission systems comprising transmitter meansincluding an oscillator capable of being swept in frequency very rapidlyover a frequency spectrum for radiating electromagnetic energy, tuningcontrol means coupled to said transmitter for sweeping said spectrumrepetitively, receiver means including said oscillator capable ofrapidly sweeping said frequency spectrum to detect electromagneticenergy from victim transmission systems, and means for automaticallyreducing the sweep rate of said transmitter and receiver means inresponse to detection of electromagnetic energy from victim transmissionsystems.
 4. An automatic sweep jamming system having a high duty cycleand rapid acquisition rate for jamming victim transmission systemscomprising transmitter means including an oscillator capable of beingswept in frequency very rapidly over a frequency spectrum for radiatingelectromagnetic energy, tuning control means coupled to said transmitterfor sweeping said spectrum repetitively, receiver means including saidoscillator capable of rapidly sweeping said frequency spectrum to detectelectromagnetic energy from victim transmission systems, and means forautomatically reducing the sweep rate of said transmitter and receivermeans in response to detection of electromagnetic energy from victimtransmission systems and returning said transmitter and receiver meansto the rapid sweep rate thereafter.
 5. In combination with an electroniccountermeasures transmitting equipment which is capable of beingcontinuously varied in frequency from a low value to a higher value toradiate jamming signals over a range of frequencies for counteringvictim transmission systems, means for automatically sweeping saidtransmitting equipment sure that the sweep rate of said equipment isslowed down while passing through detected signals from victimtransmissions and the sweep rate is returned to its normal sweep rate,said means comprising receiver means capable of rapidly sweeping a rangeof frequencies to detect signals from victim transmission systems, andmeans for automatically reducing the sweep rate of said transmittingequipment in response to detection of said victim signals.
 6. Incombination with an electronic countermeasures transmitting equipmentwhich is capable of being continuously varied in frequency from a lowvalue to a higher value to radiate jamming signals over a range offrequencies for countering victim transmission systems, means forautomatically sweeping said transmitting equipment such that the sweeprate of said equipment is slowed down while passing through detectedsignals from victim transmissions and the sweep rate is returned to itsnormal sweep rate, said means comprising receiver means including theoscillator of said transmitting equipment capable of rapidly monitoringa range of frequencies to detect signals from victim transmissionsystems, and means for automatically reducing the sweep rate of saidtransmitting equipment in response to detection of said victim signalsand returning the sweep rate to its normal sweep rate when no signalsare detected.